program Noname3;
var f1,f2:text;
    s,s1,s2,i,k,j,n,m:integer;
    mat: array[1..16,1..16] of integer;
    
begin
  assign(f1,'flip.in');
  reset(f1);
  readln(f1,n,m);
  for i:=1 to n do
   for j:=1 to m do
   read(f1,mat[i,j]);
  k:=1;

  while (k>0) do
  begin
    k:=0;
    for i:=1 to n do
    begin
    for j:=1 to m do
      if mat[i,j]>0 then s1:=s1+mat[i,j] else s2:=s2+mat[i,j];
    writeln('--------s1,s2--------',s1,s2);
    writeln;
    if abs(s2)>s1 then
      begin
        for j:=1 to m do
        mat[i,j]:=-mat[i,j];
        k:=k+1;
      end;
    s2:=0; s1:=0;
    end;
    
    
    for j:=1 to m do
    begin
    for i:=1 to 5 do
      if mat[i,j]>0 then s1:=s1+mat[i,j] else s2:=s2+mat[i,j];
    if abs(s2)>s1 then
      begin
        for i:=1 to n do
        mat[i,j]:=-mat[i,j];
        k:=k+1;
      end;
    s1:=0; s2:=0;
    end;
  end;
  
  
  for i:=1 to n do
  begin
   for j:=1 to m do
   begin
     s:=s+mat[i,j];
   end;
  end;
  assign(f2,'flip.out');
  rewrite(f2);
  writeln(f2,s);
  close(f2);
end.